The large area of low pressure centered just south of Cuba's Isle of Youth has developed enough of a well-defined circulation to be classified as Tropical Depression Sixteen, and is likely to become Tropical Storm Nicole by Wednesday. The depression has a very broad center, with little heavy thunderstorm activity near the center, and is this very dissimilar to the usual types of tropical depressions we see in the Atlantic. The large size, broad center, and lack of heavy thunderstorm activity near the center of TD 16 will limit the storm's ability to rapidly intensify. TD 16 resembles the "monsoon depressions" common in India's Bay of Bengal or the Western Pacific. A monsoon depression is similar to a regular tropical depression in the winds that it generates--about 30 - 35 mph near the outer edges (and usually stronger on the eastern side of the circulation.) Monsoon depressions have large, calm centers, and can evolve into regular tropical storms, if given enough time over water to develop a tight, closed circulation. Today's monsoon-like depression in the Caribbean was able to form because the atmospheric flow pattern of the Eastern Pacific has shifted eastwards into the Western Caribbean, bringing in the Eastern Pacific ITCZ (Intertropical Convergence Zone, a region of converging surface winds that creates a band of strong thunderstorms). This unusual flow pattern is forecast to remain in place for at least the next ten days.

An Air Force hurricane hunter aircraft has been flying at 700 feet in TD 16 since 1:30pm EDT, and has thus far found a central pressure of 999 mb. The strongest winds at flight level seen as of 3:20pm EDT were 32 mph, located about 100 miles east of the center of TD 16. Surface observations show that the strongest winds at any surface station continue to be at Buoy 42057, several hundred miles to the southeast of TD 16's center. Winds were 27 mph, gusting to 34 mph at 2:43pm EDT this afternoon. Rotation of TD 16 can be seen on radar loops out of Pico San Juan, Cuba, and well as satellite imagery. The heavy thunderstorms are currently quite disorganized, but a curved band is beginning to wrap around the north side of the center, signaling that TD 16 is growing more organized. TD 16 has brought torrential rains to the Cayman Islands, Jamaica, Cuba, and Honduras today.

Figure 1. Radar-estimated precipitation for South Florida and Cuba. TD 16 has brought 2 - 4 inches of rains to the region.

Forecast for TD 16Because TD 16 is so large, it will take more time than a typical depression for it to spin up into a strong tropical storm. Given that the steering currents are expected to pull TD 16 north-northeastwards over Cuba and into South Florida and the western Bahamas on Wednesday, the storm lacks sufficient time over water to be any stronger than a 50 mph tropical storm for Florida. TD 16 is organizing pretty slowly this afternoon, and I think the top winds in Southeast Florida are most likely to be in the 25 - 35 mph range on Wednesday. Winds are likely to be stronger in the western Bahamas, perhaps 30 - 40 mph, since they will be in the stronger right front quadrant of the storm. By the time TD 16 makes landfall in South Carolina or North Carolina on Thursday morning, it could be as strong as a 50 - 60 mph tropical storm. However, wind shear will increase sharply on Thursday as TD 16 gets caught in an upper-level trough of low pressure, and NHC is giving TD 16 only a 9% chance of making it to hurricane strength before it becomes an extratropical storm on Thursday. The primary danger from TD 16 is not wind, but heavy rainfall. A potent upper-level low and stationary front over the U.S. East Coast have been pulling moist, tropical air from the Caribbean northwards over the past few days, bringing heavy rains that have saturated the soils. This is called a Predecessor Rain Event, or PRE, since it comes in advance of the actual rain shield of the storm. (A PRE from Hurricane Karl brought southern Wisconsin the heavy rain that caused the levee on the Wisconsin River to fail yesterday.) Wilmington, NC received 10.33 inches of rain yesterday, its second greatest one-day rainfall since record keeping began in 1871. Only the 13.38" that fell during Hurricane Floyd on September 15, 1999 beat yesterday's rainfall total. With TD 16 expected to bring another 6 - 8 inches of rain to the region later this week, serious flooding is likely, and flash flood watches are posted for the North Carolina/ South Carolina border region. South Florida is also under a flood watch, for 3 - 5 inches of rain. Flooding rains of similar magnitude can also be expected in Cuba, the Cayman Islands, and the Western Bahamas through Wednesday night. Both the GFDL and HWRF models are predicting that TD 16 will dump rains in excess of eight inches along narrow portions of its path in eastern Florida, South Carolina, and North Carolina.

Up to 1,000 feared dead in Mexican landslideMexico has taken the brunt of the devastation from the hurricane season of 2010, thanks to the landfalls of this year's two deadliest and most damaging storms, Hurricanes Alex and Karl. But Mexico's worst blow yet hit this morning, when heavy rains from the remnants of Tropical Storm Matthew triggered a landslide in Mexico's mountainous Oaxaca state that buried as many as 1,000 people in Santa Maria Tlahuitoltepec, a town of 9,000. Rescuers have not reached the area yet, but hundreds are feared dead in the 300 homes that were buried by the early morning landslide. Matthew hit Belize on Saturday as a minimal tropical storm with 40 mph winds, and dissipated Sunday over southern Mexico. However, Matthew's remains stalled out over the region of Mexico that had already received torrential rains from Hurricane Karl, which hit on September 18. Satellite estimates of Matthew's rains over southern Mexico (Figure 3) show that a foot of rain may have fallen in the landslide area. Matthew's remains still linger over the region, but are probably only capable of bringing 1 - 2 inches of additional rain through Thursday.

Figure 3. Satellite-estimated rainfall for the five-day period ending at 8pm EDT Monday September 27, 2010. The dark green colors show where rainfall amounts of 300 mm (about 12 inches) fell, due to the remnants of Tropical Storm Matthew. Image credit: Navy Research Lab, Monterey.

Elsewhere in the tropicsOnce TD 16 moves out of the Caribbean, the GFS model predicts that the Western Caribbean will "reload" and produce another tropical disturbance capable of developing into a tropical depression early next week. The GFS also predicts a tropical or subtropical storm will form over the Bahamas late this week, and move north-northeast along the U.S. East Coast, missing hitting land. The NOGAPS model hints at the Bahamas storm, and also predicts development of a tropical wave a few hundred miles northeast of the Lesser Antilles Islands, about a week from now.

Hottest day in Los Angeles historyThe mercury hit a blistering 113°F (45.0°C) at 12:15 pm PDT yesterday in downtown Los Angeles, making it the hottest day in Los Angeles history. It may have gotten hotter, but the thermometer broke shortly after the record high was set. The previous record in Los Angeles was 112°F set on June 26, 1990; records go back to 1877. Nearby Long Beach tied its hottest all-time temperature yesterday, with a scorching 111°F. And Christopher C. Burt, our new featured blogger on weather records, pointed out to me that a station in the foothills at 1260' elevation near Beverly Hills owned by the Los Angeles Fire Department hit 119°F yesterday--the hottest temperature ever measured in the Los Angeles area, tying the 119°F reading from Woodland Hills on July 22, 2006. Yesterday's record heat was caused by an unusually large and intense upper-level high pressure system centered over Nevada that generated winds blowing from the land to the ocean, keeping the ocean from exerting its usual cooling influence. Remarkably, Los Angeles had its second coldest summer on record this year, and temperatures just five days ago were some the coldest September temperatures in the region for the past 50 years.

The remarkable summer of 2010Wunderground is pleased to welcome a new featured blogger--weather historian Christopher C. Burt. Chris is a leading expert in the U.S. on weather records, and is author of the world's most popular weather records book published to date, Extreme Weather: A Guide and Record Book. He's spent a lifetime collaborating with like-minded individuals from around the world, and no one--including official sources such as the National Climatic Data Center and the National Extremes Committee--has done as thorough a job correlating the various weather records available and determining the most accurate extreme values of such. Each month he'll be reporting on the notable records for heat, cold, and precipitation set world-wide, and his first post takes a look at the remarkable summer of 2010. It's great to have someone like Chris who stays on top of weather extremes, and I hope you'll pay a visit to his blog and welcome him to the wunderground site!

"Hurricane Haven" airing this afternoonMy live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

The question of the night is apparently "Are the schools closed? lol..I hope, wherever you are, that you get a last minute reprieve from the governor(school board) and you get that school close at 11. SC at 11!! I'm glad that's the question of the night....though I'm concerned about heavy rains in the mountains of Jamaica.

I see two spins on this loop. One looks like the llc at aroung 20n 83w diving se toward the convection. The other looking like a mlc at around 22n 81w. I think this may be having vertical stacking issues.

Quoting MZT:Right now I think 50/50 chance this never gets named. TS winds forecast to be well offshore... rather non-tropical pattern to it. Will probably begin to look like a hook-shaped nor'easter by the time it approaches N.C.

Disagree. Winds will catch up to the pressure enough before transition, imo.

Quoting jambev:Montego Bay is reporting light but steady rain falling.Here in Kingston, we have had several fast moving squalls but currently not raining.The main convection now seems to be over us especially in the west.This is one strange system.

Good to see a fellow Jamaican blogger, currently in my location there's a light drizzle with pressure fluctuating around 1002 mbar, winds calm.

Quoting BahaHurican:On the pple drowning in flooding in FL, u need to get real. It doesn't even need to be a hurricane - all that has to happen is that the flooding be enough to cause someone to get into one of those "drainage" pools or a canal. Every year there are flooding related deaths in SFL because people can't tell where the road ends and the canal begins - and they drive in and DROWN.

Don't downplay the danger. Just because FL is flat, it can't be assumed that the risks are nil.

Yes, people drown by driving into canals, but not because of flooding; they drive into canals because blinding rain has obscured their vision, because they are distracted, because they are drunk, because they lose control of their cars for a host of other reasons, but not because of flooding.

Difficult though it may be, think for a moment. Flooded roads slow a car's momentum and stall its engine; they do not cause it to accelerate into a canal.

Floods lead to intersection drowning deaths in most parts of the country, but not here.

Quoting stormpetrol:My personal take on TD#16 , it is actually 2 separate systems, the official one IMO will not amount to much wind wise(Rain&flooding yes), The mean COC is around 18N/79W maybe off a degree, but personally I think this is main area greatest concern, JMO. THis has the greatest potential IMO opinion to become a dangerous system windwise and otherwise!

That may have been what the models were trying to pick up on, but got confuzzled. Too much activity all in one area.

Quoting surfmom:what are the "consequences" if any for the "incorrect"?

"It shows the 1004 mb isobar passing right through Grand Cayman approximately yet we know that all afternoon and currently the pressure has been sub 1000 mb. In fact it is 998 right now. Who comes up with these images and on what basis ?. This one is obviously incorrect".

If you are still on, I think the L is 995mb as of the last advisory for reasons already mentioned.

Winds generally "catch up" to the pressure, so it is significant in that regard.

That being said, as large as the system is, that will take a long time, so it is not the same as a "normal" system.

Quoting stormpetrol:My personal take on TD#16 , it is actually 2 separate systems, the official one IMO will not amount to much wind wise(Rain&flooding yes), The mean COC is around 18N/79W maybe off a degree, but personally I think this is main area greatest concern, JMO. THis has the greatest potential IMO opinion to become a dangerous system windwise and otherwise!

My personal take on TD#16 , it is actually 2 separate systems, the official one IMO will not amount to much wind wise(Rain&flooding yes), The mean COC is around 18N/79W maybe off a degree, but personally I think this is main area greatest concern, JMO. THis has the greatest potential IMO opinion to become a dangerous system windwise and otherwise!

Quoting jambev:Montego Bay is reporting light but steady rain falling.Here in Kingston, we have had several fast moving squalls but currently not raining.The main convection now seems to be over us especially in the west.This is one strange system.

Right now I think 50/50 chance this never gets named. TS winds forecast to be well offshore... rather non-tropical pattern to it. Will probably begin to look like a hook-shaped nor'easter by the time it approaches N.C.

Quoting jambev:Montego Bay is reporting light but steady rain falling.Here in Kingston, we have had several fast moving squalls but currently not raining.The main convection now seems to be over us especially in the west.This is one strange system.

Thanks Bev.Western Jam. could get some real heavy rain for the next few hrs...

The Meteorological Service has extended the Flash Flood Warning for low-lying and flood prone areas of all parishes until 5:00 p.m. tomorrow.

A FLASH FLOOD WARNING means flooding has been reported or will occur shortly. Motorists and pedestrians should not attempt to cross flooded roadways or other low-lying areas as strong currents are likely. Residents in low-lying areas should be on the alert for rising waters and be ready to move quickly to higher ground.

Through today, radar reports indicate that light to moderate showers affected all parishes as well as offshore areas of the northwest and south coasts. Widespread showers and thunderstorms are forecast to peak within the next 24 hours but continue to affect the island at least until Friday.

Due to the proximity of Tropical Depression #16 northwest of Jamaica, fishers and other marine interests, particularly over northwestern and southern waters, are being advised not to venture far from port as above-normal wave heights and strong gusty winds are likely.

At 4:00 p.m. the centre of Tropical Depression #16 was located near latitude 21.5 degrees north and longitude 82.4 degrees west or about 190 kilometres south of Havana, Cuba.

The Depression is moving toward the north-northeast near 17 km/h. On the forecast track, the centre of the tropical cyclone will cross Cuba tonight and be near or over southeastern Florida by Wednesday afternoon. However, in this case, most of the strong winds and heavy rains are occurring a couple hundred miles to the east and southeast of the centre.

Maximum sustained winds are near 55 km/h, with higher gusts. Some strengthening is forecast during the next 12 to 24 hours and the Depression is expected to become a tropical storm tonight or Wednesday before merging with a frontal zone on Thursday.

The Meteorological Service will continue to monitor the progress of this system.

While I agree that it has been a very active season, my biggest concern is that the general public does not view it the same as most of us on the blog.

Not wanting anyone to get hit with a major, however with all of the doom and gloom that was predicted this year for U.S. land falling hurricanes, the level of complacency is guaranteed to rise within the general public.

This could be the worst thing that comes out of this season!

Chuck

Agreed -- what happens if a truly strong storm heads our way? So many have been minimal or bypassed us, that people will write it off and not prepare.

Montego Bay is reporting light but steady rain falling.Here in Kingston, we have had several fast moving squalls but currently not raining.The main convection now seems to be over us especially in the west.This is one strange system.